Striated muscle in Duchenne's dystrophy is characterized by the presence of scattered foci of degenerating myofibers. Within these foci, numerous myogenic cells in various stages of regeneration represent the muscles potential for repair. In older patients (less than 5 years), regeneration become abnormal and eventually has no influence on the clinical progress of dystrophic degeneration. It is proposed that in early stages of the disease, only mature regenerating fibers succumb to the pathological defect, while later regenerative failure is due to a direct affect upon the myogenic stem cell. The aim of the proposed study is to analyze the nature and influence of the regenerative response in the progression of Duchenne's dystrophy. Toward this end, the population, distribution and behavior of satellite cells will be examined in both human and murine dystrophies. In addition to the structural and morphometric studies on biopsies, the dynamics of satellite cell development will be analyzed in clonal tissue culture. It is suggested that the demonstrated myoblast to fibroblast modulation accounts for the characteristic loss of regenerating stem cells and the simultaneous increase in interstitial fibrosis. Based on studies which reveal the potential for structural and functional alterations of the myogenic component, subsequent investigations will examine the influence of a diseased environment on the differentiation and metabolism of satellite cells. Additional studies will examine the structural alteration of the connective tissue and vasculature in normal and dystrophic muscle.